Written by Emily Green
Have you ever wondered why for some people it is necessary to eat a larger amount of food to support weight restoration in eating disorder recovery? Why is it that some people might need up to 4000 calories a day (or more) just to maintain or restore weight?
What is hypermetabolism?
To understand hypermetabolism, let's first define normal metabolism. Metabolism is a term encompassing all the life-sustaining physical and chemical processes that occur in the body which are necessary to keep it functioning on a day-to-day basis. It is regulated by our nervous system and hormones which act as chemical messengers in our body.
This is not to be confused with the metabolic rate which is the total amount of energy needed for these physical and chemical processes (like breathing, heart rate and cell production) to run. Metabolic rate is measured in either calories or kilojoules (1 kcal = 4.184kJ).
With this in mind, hypermetabolism is a state of accelerated metabolic activity which can cause symptoms such as night sweats, elevated or irregular heartbeat, insomnia, fatigue, anaemia, weight loss, shortness of breath or nervous system dysfunction (1).
Similarly, there is an opposite term, hypometabolism, ‘hypo’ meaning ‘less’ or ‘lower’ so hypometabolism refers to a decreased metabolic rate.
Hypermetabolism in eating disorders
In many eating disorders, such as anorexia nervosa (AN), bulimia nervosa (BN) and Other Specified Feeding or Eating Disorder (OSFED), food intake can be significantly reduced and below an individual's energy needs. When the human body isn't receiving enough energy from food, in order to stay alive it will start to shut down many of those physical and chemical processes (i.e. metabolism slows down and enters a hypometabolic state) which can result in many physical and psychological side effects.
This is also known as starvation syndrome, or adaptive thermogenesis, and provides an explanation as to why many people with restrictive eating disorders develop symptoms such as constipation, hair falling out, amenorrhea (loss of menstrual cycle), poor concentration or mood swings. Many side effects are a result of starvation and hypometabolism, not a symptom of having an eating disorder.
As demonstrated in the Minnesota Starvation Experiment, underfeeding resulted in metabolism dropping by approximately 40% (2). In a more recent study, the mean basal metabolic rate (BMR) was 21% lower in individuals with anorexia nervosa than in controls (3).
In eating disorder recovery, when a person starts nourishing their body again, metabolism speeds up as the body begins to use the energy from food to power physical and chemical processes which might have been on power saving mode. In some people, this process might speed up significantly and hypermetabolism occurs. As the body is using more energy to power body functions, build muscle and tissue and restore weight (if needed) this will require more energy to be consumed.
It is important to note that a person's experience of hypermetabolism might look different from someone else. There is no simple way to detect the rate of hypermetabolism or how much energy you will ultimately need, rather as clinicians we monitor symptoms and results and adjust our recommendations accordingly.
Does hypermetabolism only occur in eating disorders?
A hypermetabolic state can last a few weeks during recovery from an eating disorder and can happen both in the community and hospital setting. Regardless of the setting, it is important to seek advice from a registered dietitian or medical professional in the early stages of nutritional rehabilitation. Hypermetabolism is a symptom of an underlying problem so isn't just seen in eating disorder recovery.
Hypermetabolism is commonly seen in people with severe burns, sepsis, post-surgery or traumatic injury during recovery (1). For context, a person with severe burns over 40% of their body can have an increased metabolism at 140% of their normal rate, decreasing to 110% even 12 months after admission (4). This gives insight into the amount of energy required for the body to heal and why we see higher energy requirements for some people in eating disorder recovery.
How does hypermetabolism impact my meal plan?
If you are experiencing hypermetabolism you will need to adjust your intake to meet the energy needs of your body. In practice, we know that this could range anywhere from 30-40kcal/kg/d up to 70-100kcal/kg/day (5). Guidance from NICE on anorexia nervosa treatment advises that to achieve weight restoration of 0.5-1kg per week, a person will require an additional up to 3500-7000 additional calories spread across the week (average of 500-1000 calories per day) (6).
Some people might find it difficult to meet these energy requirements through food alone, especially in the early days when digestive issues are commonly experienced. Nutrition supplement drinks can be a helpful addition to a meal plan in the short term to reduce total volume of food/fluids while meeting energy requirements. Some people experience a rise in hunger, and others experience early satiety so it is best to work with a registered dietitian to come up with an eating plan that works for you.
Taking the first step towards eating disorder recovery can feel huge and daunting. We get it. If you would benefit from specialist support through your recovery journey we invite you to book a free 15 minute discovery call with one of our eating disorder dietitians at the TC Nutrition Clinic to discuss how we can support you.
Emily is studying MSc Clinical Nutrition, after having graduated from a degree in Nutrition & Psychology from Newcastle University. She has an interest in supporting people to overcome disordered eating, find food freedom and keep a healthy mind. You can find Emily on Instagram @nutritionupontyne and on her blog nutritionupontyne.co.uk
Peete, C., 2022. What is hypermetabolism? [online] The Health Board. Available at: <https://www.thehealthboard.com/what-is-hypermetabolism> [Accessed 16 August 2022].
Keys, A., Brozek, J., Henshel, A., Mickelson, O., & Taylor, H.L. 1950. The biology of human starvation, (Vols. 1–2). University of Minnesota Press. Minneapolis, MN
Polito, A., Fabbri, A., Ferro-Luzzi, A., Cuzzolaro, M., Censi, L., Ciarapica, D., Fabbrini, E. and Giannini, D., 2000. Basal metabolic rate in anorexia nervosa: relation to body composition and leptin concentrations. The American Journal of Clinical Nutrition, [online] 71(6), pp.1495-1502. Available at: <https://academic.oup.com/ajcn/article/71/6/1495/4729462> [Accessed 15 August 2022].
Williams, F., Herndon, D. and Jeschke, M., 2009. The Hypermetabolic Response to Burn Injury and Interventions to Modify this Response. Clinics in Plastic Surgery, [online] 36(4), pp.583-596. Available at: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3776603> [Accessed 19 August 2022].
Marzola, E., Nasser, J., Hashim, S., Shih, P. and Kaye, W., 2013. Nutritional rehabilitation in anorexia nervosa: review of the literature and implications for treatment. BMC Psychiatry, [online] 13(1). Available at: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3829207/> [Accessed 17 August 2022].
National Collaborating Centre for Mental Health (UK), 2004. Eating Disorders: Core Interventions in the Treatment and Management of Anorexia Nervosa, Bulimia Nervosa and Related Eating Disorders.. Leicester: British Psychological Society.
Talia Cecchele Nutrition is a team of registered dietitians that specialise in eating disorders, disordered eating, gut health and sports nutrition. We aim to bring balance back to nutrition, help you to break free from food rules and find food freedom. We offer virtual consultations and group programs so whether you are based in London, the United Kingdom or around the world we would love to support you. To enquire about a private consultation please fill out a contact form.
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